Put flour, butter, 50 g sugar and egg yolk in a bowl. Knead first with the dough hooks of the hand mixer, then with your hands to a smooth short pastry. Wrap the dough in foil and chill for about 30 minutes.
Sort blueberries and blackberries, wash and drain well. Put 125 g blueberries and 200 g blackberries into a high mixing bowl and puree finely. Mix quark, cream cheese, eggs, pudding powder, 200 g sugar and berry puree.
Roll out the shortcrust pastry on a floured work surface and place it in a greased springform pan (18 cm Ø). Add the cheese mixture and smooth it down. In a preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see
manufacturer) bake for about 1 1/2 hours. Remove and let cool on a cake rack for about 1 hour. Carefully remove from the tin and let it cool down.
Whip the cream with the whisks of the hand mixer until stiff. Spread the cream on the cheesecake and garnish with the remaining berries.